Method and apparatus for transmitting location estimation message in wireless communication system

ABSTRACT

Provided are a method and an apparatus for transmitting a message through a terminal in a wireless communication system. The terminal receives positioning reference signals (PRS) from a reference cell and at least one of the neighbor cells, receives an auxiliary data provision message including a reference cell PRS muting sequence for indicating a muting pattern of the PRS transmitted through the reference cell and a neighbor cell PRS muting sequence for indicating the muting pattern of the PRS transmitted through at least one of the neighbor cells from an enhanced serving mobile location center (E-SMLC), and transmits a reference signal time difference (RSTD) measured on the basis of the PRS received from the reference cell and the at least one of the neighbor cells to the E-SMLC.

This application is a continuation of application Ser. No. 13/808,880,filed Jan. 7, 2013, which is a 371 National Stage Entry of InternationalApplication No. PCT/KR2011/005273, filed Jul. 18, 2011, and claims thebenefit of U.S. Provisional Application Nos. 61/364,818, filed Jul. 16,2010, 61/440,837, filed Feb. 8, 2011 and 61/444,122, filed Feb. 17,2011, all of which are incorporated by reference in their entiretyherein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a message transmission method and apparatus forlocation estimation in a wireless communication system.

Related Art

User equipment (UE) positioning for estimating a location of a UE hasrecently been used for various usages in real life, which requires amore accurate UE positioning method. The UE positioning method can beroughly classified into four methods as follows.

1) Global positioning system (GPS)-based method: In this method, asatellite is used to estimate the location of the UE. Information mustbe received from at least four satellites. Disadvantageously, thismethod cannot be used in an indoor environment.

2) Terrestrial positioning-based method: In this method, the location ofthe UE is estimated by using a timing difference of signals transmittedfrom base stations (BSs). Signals must be received from at least threeBSs. Although this method has lower location estimation performance incomparison with the GPS-based method, it can be used in most ofenvironments. A signal received from the BS may be a synchronizationsignal or a reference signal (RS), and according to a wirelesscommunication system in use, can be defined in various terms, such asobserved time difference of arrival (OTDOA) in UMTS terrestrial radioaccess network (UTRAN), enhanced observed time difference (E-OTD) inGSM/EDGE radio access network (GERAN), advanced forward linktrilateration (AFLT) in CDMA2000, etc.

The RS can be used to estimate the location of the UE. The RS mayinclude a synchronization signal. The UE can receive RSs transmittedfrom multiple cells, and can use a difference in a time delay of eachsignal. The UE may report the difference in the time delay to the BS sothat the BS can calculate the location of the UE, or may autonomouslycalculate the location of the UE. Referring to the section 4.1.1 of 3rdgeneration partnership project (3GPP) long term evolution (LTE) TS36.355V9.0.0 (2009 December), an enhanced serving mobile location center(E-SMLC) can use a LTE positioning protocol (LPP) to control measurementvalues such as a reference signal time difference (RSTD) measured by theUE. The LPP can be defined as a point-to-point between a location server(e.g., E-SMLC, etc.) and a target device (i.e., UE, etc.) so that alocation of the target device can be estimated using a location relationmeasurement value obtained from one or more RSs.

Meanwhile, RS transmission for UE location estimation may be muted. Thatis, a cell may not transmit the RS in a specific situation. This isbecause, when the UE receives an RS from a reference cell or a neighborcell, strength of an RS received from the reference cell may besignificantly greater than strength of an RS received from the neighborcell, and in this case, the RS received from the neighbor cell may notbe properly decoded. The UE needs to exactly know a muting pattern ofRSs transmitted from multiple cells. The UE can recognize a mutingpattern of an RS of each cell on the basis of at least one cell.However, due to such a reason as a handover of the UE or an asynchronousnetwork or the like, there is a possibility that ambiguity occurs inwhich the UE cannot accurately recognize a muting pattern of an RStransmitted by each cell.

Accordingly, there is a need for a message configuration andtransmission method by which a UE recognizes a muting pattern of an RS.

SUMMARY OF THE INVENTION

The present invention provides a message transmission method andapparatus for location estimation in a wireless communication system.The present invention also provides a message configuration method and amessage transmission method for solving a system frame number (SFN)unknown problem when estimating a location of a terminal in a wirelesscommunication system.

In an aspect, a method of transmitting a message by a terminal in awireless communication system is provided. The method includes receivinga positioning reference signal (PRS) from each of a reference cell andat least one of neighbor cell, receiving from an enhanced serving mobilelocation center (E-SMLC) an assistance data provide message including areference cell PRS muting sequence for indicating a muting pattern ofthe PRS transmitted by the reference cell and a neighbor cell PRS mutingsequence for indicating a muting pattern of a PRS transmitted by the atleast one of the neighbor cell, and transmitting to the E-SMLC areference signal time difference (RSTD) measured on the basis of the PRSreceived from the reference cell or the at least one neighbor cell.

The reference cell muting sequence and the neighbor cell muting sequencemay be configured on the basis of a system frame number (SFN) of a cellfor which the SFN can be obtained by the terminal at a time of receivingthe assistance data provide message.

The cell for which the SFN can be obtained by the terminal may be aserving cell for providing a service to the terminal.

A first bit of the reference cell muting sequence and the neighbor cellmuting sequence may correspond to a first PRS occasion after the SFN ofthe cell for which the SFN can be obtained becomes 0.

The reference cell muting sequence and the neighbor cell muting sequencenay be configured on the basis of a time of receiving the assistancedata provide message.

A first bit of the reference cell muting sequence and the neighbor cellmuting sequence may correspond to a first PRS occasion after theassistance data provide message is received.

The reference cell muting sequence and the neighbor cell muting sequencemay be configured on the basis of an SFN of the reference cell obtainedby decoding a physical broadcast channel (PBCH) transmitted from thereference cell.

Bits constituting the reference cell muting sequence or the neighborcell muting sequence may be all 1 or 0.

The RSTD may be a relative delay of a reference subframe including thePRS received from the reference cell and a neighbor subframe includingthe PRS received from the at least one neighbor cell and correspondingto the reference subframe.

The method may further include transmitting to the E-SMLC an assistancedata request message for requesting the assistance data provide message.

In another aspect, a terminal in a wireless communication system isprovided. The terminal includes a radio frequency (RF) unit fortransmitting or receiving a radio signal, and a processor coupled to theRF unit. The processor is configured for receiving a positioningreference signal (PRS) from each of a reference cell and at least one ofneighbor cell, receiving from an enhanced serving mobile location center(E-SMLC) an assistance data provide message including a reference cellPRS muting sequence for indicating a muting pattern of the PRStransmitted by the reference cell and a neighbor cell PRS mutingsequence for indicating a muting pattern of a PRS transmitted by the atleast one of the neighbor cell, and transmitting to the E-SMLC areference signal time difference (RSTD) measured on the basis of the PRSreceived from the reference cell or the at least one neighbor cell.

According to the present invention, a terminal can correctly recognize amuting pattern of a positioning reference signal (PRS) transmitted byeach cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

FIG. 3 shows an example of a resource grid of a single downlink slot.

FIG. 4 shows the structure of a downlink subframe.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 and FIG. 7 show an example of a PRS pattern mapped to a resourceblock.

FIG. 8 shows an example of operating an observed time difference ofarrival (OTDOA) method as a terrestrial positioning-based method.

FIG. 9 shows another example of operating a downlink OTDOA method as aterrestrial positioning-based method.

FIG. 10 shows an example of an assistance data exchange process betweena UE and an E-SMLC through an LPP.

FIG. 11 shows an example of a data exchange process between a BS and anE-SMLC through an LPPa.

FIG. 12 and FIG. 13 show an example of a case where an SFN unknownproblem occurs.

FIG. 14 shows the proposed message transmission method for locationestimation according to an embodiment of the present invention.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following technique may be used for various wireless communicationsystems such as code division multiple access (CDMA), a frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), singlecarrier-frequency division multiple access (SC-FDMA), and the like. TheCDMA may be implemented as a radio technology such as universalterrestrial radio access (UTRA) or CDMA2000. The TDMA may be implementedas a radio technology such as a global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, E-UTRA (evolved UTRA), andthe like. IEEE 802.16m, an evolution of IEEE 802.16e, provides backwardcompatibility with a system based on IEEE 802.16e. The UTRA is part of auniversal mobile telecommunications system (UMTS). 3GPP (3rd generationpartnership project) LTE (long term evolution) is part of an evolvedUMTS (E-UMTS) using the E-UTRA, which employs the OFDMA in downlink andthe SC-FDMA in uplink. LTE-A (advanced) is an evolution of 3GPP LTE.

Hereinafter, for clarification, LTE-A will be largely described, but thetechnical concept of the present invention is not meant to be limitedthereto.

FIG. 1 shows a wireless communication system.

The wireless communication system 10 includes at least one base station(BS) 11. Respective BSs 11 provide a communication service to particulargeographical areas 15 a, 15 b, and 15 c (which are generally calledcells). Each cell may be divided into a plurality of areas (which arecalled sectors). A user equipment (UE) 12 may be fixed or mobile and maybe referred to by other names such as MS (mobile station), MT (mobileterminal), UT (user terminal), SS (subscriber station), wireless device,PDA (personal digital assistant), wireless modem, handheld device. TheBS 11 generally refers to a fixed station that communicates with the UE12 and may be called by other names such as eNB (evolved-NodeB), BTS(base transceiver system), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. A BS providing a communication service to theserving cell is called a serving BS. The wireless communication systemis a cellular system, so a different cell adjacent to the serving cellexists. The different cell adjacent to the serving cell is called aneighbor cell. A BS providing a communication service to the neighborcell is called a neighbor BS. The serving cell and the neighbor cell arerelatively determined based on a UE.

This technique can be used for downlink or uplink. In general, downlinkrefers to communication from the BS 11 to the UE 12, and uplink refersto communication from the UE 12 to the BS 11. In downlink, a transmittermay be part of the BS 11 and a receiver may be part of the UE 12. Inuplink, a transmitter may be part of the UE 12 and a receiver may bepart of the BS 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

It may be referred to Paragraph 5 of “Technical Specification GroupRadio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation (Release 8)” to 3GPP (3rdgeneration partnership project) TS 36.211 V8.2.0 (2008-03). Referring toFIG. 2, the radio frame includes 10 subframes, and one subframe includestwo slots. The slots in the radio frame are numbered by #0 to #19. Atime taken for transmitting one subframe is called a transmission timeinterval (TTI). The TTI may be a scheduling unit for a datatransmission. For example, a radio frame may have a length of 10 ms, asubframe may have a length of 1 ms, and a slot may have a length of 0.5ms.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain and a plurality ofsubcarriers in a frequency domain. Since 3GPP LTE uses OFDMA indownlink, the OFDM symbols are used to express a symbol period. The OFDMsymbols may be called by other names depending on a multiple-accessscheme. For example, when a single carrier frequency division multipleaccess (SC-FDMA) is in use as an uplink multi-access scheme, the OFDMsymbols may be called SC-FDMA symbols. A resource block (RB), a resourceallocation unit, includes a plurality of continuous subcarriers in aslot. The structure of the radio frame is merely an example. Namely, thenumber of subframes included in a radio frame, the number of slotsincluded in a subframe, or the number of OFDM symbols included in a slotmay vary.

3GPP LTE defines that one slot includes seven OFDM symbols in a normalcyclic prefix (CP) and one slot includes six OFDM symbols in an extendedCP.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, an uplink transmission and a downlinktransmission are made at different frequency bands. According to the TDDscheme, an uplink transmission and a downlink transmission are madeduring different periods of time at the same frequency band. A channelresponse of the TDD scheme is substantially reciprocal. This means thata downlink channel response and an uplink channel response are almostthe same in a given frequency band. Thus, the TDD-based wirelesscommunication system is advantageous in that the downlink channelresponse can be obtained from the uplink channel response. In the TDDscheme, the entire frequency band is time-divided for uplink anddownlink transmissions, so a downlink transmission by the BS and anuplink transmission by the UE can be simultaneously performed. In a TDDsystem in which an uplink transmission and a downlink transmission arediscriminated in units of subframes, the uplink transmission and thedownlink transmission are performed in different subframes.

FIG. 3 shows an example of a resource grid of a single downlink slot.

A downlink slot includes a plurality of OFDM symbols in the time domainand N_(RB) number of resource blocks (RBs) in the frequency domain. TheN_(RB) number of resource blocks included in the downlink slot isdependent upon a downlink transmission bandwidth set in a cell. Forexample, in an LTE system, N_(RB) may be any one of 60 to 110. Oneresource block includes a plurality of subcarriers in the frequencydomain. An uplink slot may have the same structure as that of thedownlink slot.

Each element on the resource grid is called a resource element. Theresource elements on the resource grid can be discriminated by a pair ofindexes (k,l) in the slot. Here, k (k=0, . . . , N_(RB)×12−1) is asubcarrier index in the frequency domain, and l is an OFDM symbol indexin the time domain.

Here, it is illustrated that one resource block includes 7×12 resourceelements made up of seven OFDM symbols in the time domain and twelvesubcarriers in the frequency domain, but the number of OFDM symbols andthe number of subcarriers in the resource block are not limited thereto.The number of OFDM symbols and the number of subcarriers may varydepending on the length of a cyclic prefix (CP), frequency spacing, andthe like. For example, in case of a normal CP, the number of OFDMsymbols is 7, and in case of an extended CP, the number of OFDM symbolsis 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively usedas the number of subcarriers in one OFDM symbol.

FIG. 4 shows the structure of a downlink subframe.

A downlink subframe includes two slots in the time domain, and each ofthe slots includes seven OFDM symbols in the normal CP. First three OFDMsymbols (maximum four OFDM symbols with respect to a 1.4 MHz bandwidth)of a first slot in the subframe corresponds to a control region to whichcontrol channels are allocated, and the other remaining OFDM symbolscorrespond to a data region to which a physical downlink shared channel(PDSCH) is allocated.

The PDCCH may carry a transmission format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a PCH, systeminformation on a DL-SCH, a resource allocation of an higher layercontrol message such as a random access response transmitted via aPDSCH, a set of transmission power control commands with respect toindividual UEs in a certain UE group, an activation of a voice overinternet protocol (VoIP), and the like. A plurality of PDCCHs may betransmitted in the control region, and a UE can monitor a plurality ofPDCCHs. The PDCCHs are transmitted on one or an aggregation of aplurality of consecutive control channel elements (CCE). The CCE is alogical allocation unit used to provide a coding rate according to thestate of a wireless channel. The CCE corresponds to a plurality ofresource element groups. The format of the PDCCH and an available numberof bits of the PDCCH are determined according to an associative relationbetween the number of the CCEs and a coding rate provided by the CCEs.

The BS determines a PDCCH format according to a DCI to be transmitted tothe UE, and attaches a cyclic redundancy check (CRC) to the DCI. Aunique radio network temporary identifier (RNTI) is masked on the CRCaccording to the owner or the purpose of the PDCCH. In case of a PDCCHfor a particular UE, a unique identifier, e.g., a cell-RNTI (C-RNTI), ofthe UE, may be masked on the CRC. Or, in case of a PDCCH for a pagingmessage, a paging indication identifier, e.g., a paging-RNTI (P-RNTI),may be masked on the CRC. In case of a PDCCH for a system informationblock (SIB), a system information identifier, e.g., a systeminformation-RNTI (SI-RNTI), may be masked on the CRC. In order toindicate a random access response, i.e., a response to a transmission ofa random access preamble of the UE, a random access-RNTI (RA-RNTI) maybe masked on the CRC.

FIG. 5 shows the structure of an uplink subframe.

An uplink subframe may be divided into a control region and a dataregion in the frequency domain. A physical uplink control channel(PUCCH) for transmitting uplink control information is allocated to thecontrol region. A physical uplink shared channel (PUCCH) fortransmitting data is allocated to the data region. If indicated by ahigher layer, the user equipment may support simultaneous transmissionof the PUCCH and the PUSCH.

The PUCCH for one UE is allocated in an RB pair. RBs belonging to the RBpair occupy different subcarriers in each of a 1^(St) slot and a 2^(nd)slot. A frequency occupied by the RBs belonging to the RB pair allocatedto the PUCCH changes at a slot boundary. This is called that the RB pairallocated to the PUCCH is frequency-hopped at a slot boundary. Since theUE transmits UL control information over time through differentsubcarriers, a frequency diversity gain can be obtained. In the figure,m is a location index indicating a logical frequency-domain location ofthe RB pair allocated to the PUCCH in the subframe.

Uplink control information transmitted on the PUCCH may include a HARQACK/NACK, a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR) which is an uplink radioresource allocation request, and the like.

The PUSCH is mapped to a uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

Hereinafter, a reference signal is described below.

A reference signal is generally transmitted as a sequence. A referencesignal sequence is not particularly limited and a certain sequence maybe used as the reference signal sequence. As the reference signalsequence, a sequence generated through a computer based on phase shiftkeying (PSK) (i.e., a PSK-based computer generated sequence) may beused. The PSK may include, for example, binary phase shift keying(BPSK), quadrature phase shift keying (QPSK), and the like. Or, as thereference signal sequence, a constant amplitude zero auto-correlation(CAZAC) may be used. The CAZAC sequence may include, for example, aZadoff-Chu (ZC)-based sequence, a ZC sequence with cyclic extension, aZC sequence with truncation, and the like. Also, as the reference signalsequence, a pseudo-random (PN) sequence may be used. The PN sequence mayinclude, for example, an m-sequence, a sequence generated through acomputer, a gold sequence, a Kasami sequence, and the like. Also, acyclically shifted sequence may be used as the reference signalsequence.

A downlink reference signal (RS) can be classified into a cell-specificRS (CRS), a multimedia broadcast and multicast single frequency network(MBSFN) RS, a UE-specific RS, a positioning RS (PRS), and a channelstate information (CSI) RS (CSI-RS). The CRS is an RS transmitted to allUEs in a cell, and can be used in both data demodulation and channelestimation. The CRS can be transmitted in all downlink subframes in acell supporting PDSCH transmission. The MBSFN RS is an RS for providinga multimedia broadcast multicast service (MBMS), and can be transmittedin a subframe allocated for MBSFN transmission. The MBSFN RS can bedefined only in an extended cyclic prefix (CP) structure. TheUE-specific RS is an RS received by a specific UE or a specific UE groupin the cell, and can also be called a dedicated RS (DRS). Alternatively,the UE-specific RS can also be called a demodulation RS (DMRS) since itis primarily used in data demodulation of a specific UE or a specific UEgroup. The CSI-RS can be used for estimation of channel stateinformation in a 3GPP LTE-A system. The CSI-RS is relatively sparelyarranged in a frequency domain or a time domain. The CSI-RS can bepunctured in a data region of a normal subframe or an MBSFN subframe. Ifrequired, a channel quality indicator (CQI), a precoding matrixindicator (PMI), a rank indicator (RI), etc., can be reported from theUE through CSI estimation. The CSI-RS can be transmitted through 1, 2,4, or 8 antenna ports.

The PRS is an RS defined for UE location estimation. The PRS can betransmitted through a resource block in a downlink subframe configuredfor PRS transmission. The downlink subframe configured for PRStransmission can also be called a positioning subframe. If the normalsubframe and the MBSFN subframe are both configured as positioningsubframes in a cell, an OFDM symbol configured for PRS transmission inthe MBSFN subframe uses the same CP structure as that used in a firstsubframe of a radio frame. If only the MBSFN subframe is configured asthe positioning subframe in the cell, the OFDM symbol configured for PRStransmission uses an extended CP structure. The PRS is not mapped to aresource element to which a physical broadcast channel (PBCH), a primarysynchronization signal (PSS), or a secondary synchronization signal(SSS) is mapped. In addition, the PRS can be defined for Δf=15 kHz.

A PRS sequence can be defined by Equation 1 below.

         ⟨Equation  1⟩${r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}$

In Equation 1, n_(s) denotes a slot number in a radio frame, and ldenotes an OFDM symbol number in a slot. m is 0, 1, . . . , 2N_(RB)^(max,DL)−1. 2N_(RB) ^(max,DL) denotes the number of resource blockscorresponding to a maximum bandwidth in a downlink. For example, 2N_(RB)^(max,DL) is 110 in 3GPP LTE. c(i) is a PN sequence and is apseudo-random sequence. The PN sequence can be defined by a length−31gold sequence. Equation 2 shows an example of the gold sequence c(n).c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C)))mod 2x ₁(n+31)=(x ₁(n+3)+(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n)mod 2  <Equation 2>

Herein, Nc is 1600, x(i) is a first m-sequence, and y(i) is a secondm-sequence. For example, the first m-sequence or the second m-sequencemay be initialized in each OFDM symbol according to a cell ID, a slotnumber in a radio frame, an OFDM symbol index in a slot, a CP type, etc.A pseudo-random sequence generator can be initialized asc_(init)=2¹⁰·(7·(n_(s)+1)+l+1)·(2·N_(ID) ^(cell)+1)+2·N_(ID)^(cell)+N_(CP) at the start of each radio frame. In case of a normal CP,N_(CP) is 1. In case of an extended CP, N_(CP) is 0.

A PRS sequence r_(l,ns)(m) can be mapped to a complex modulation symbola_(k,l) ^((p)) in a slot n_(s) according to Equation 3.a _(k,l) ^((p)) −r _(l,n) _(s) (m′)  <Equation 3>

In a normal CP case, k, l, m, m′ of Equation 3 can be determined byEquation 4.

          ⟨Equation  4⟩  k = 6(m + N_(RB)^(DL) − N_(RB)^(PRS)) + (6 − l + v_(shift))mod 6$l = \left\{ {{{\begin{matrix}{3,5,6} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2,3,5,6} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}\left( {1\mspace{14mu}{or}\mspace{14mu} 2\mspace{14mu}{PBCH}\mspace{14mu}{antenna}\mspace{14mu}{ports}} \right)}} \\{2,3,5,6} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}\left( {4\mspace{14mu}{PBCH}\mspace{14mu}{antenna}\mspace{14mu}{ports}} \right)}}\end{matrix}\mspace{20mu} m} = 0},1,\ldots\mspace{11mu},{{{2 \cdot N_{RB}^{PRS}} - {1\mspace{20mu} m^{\prime}}} = {m + N_{RB}^{\max,{DL}} - N_{RB}^{PRS}}}} \right.$

In an extended CP case, k, l, m, m′ of Equation 3 can be determined byEquation 5.

          ⟨Equation  5⟩  k = 6(m + N_(RB)^(DL) − N_(RB)^(PRS)) + (5 − l + v_(shift))mod 6$l = \left\{ {{{\begin{matrix}{4,5} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2,4,5} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}\left( {1\mspace{14mu}{or}\mspace{14mu} 2\mspace{14mu}{PBCH}\mspace{14mu}{antenna}\mspace{14mu}{ports}} \right)}} \\{2,4,5} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}\left( {4\mspace{14mu}{PBCH}\mspace{14mu}{antenna}\mspace{14mu}{ports}} \right)}}\end{matrix}\mspace{20mu} m} = 0},1,\ldots\mspace{11mu},{{{2 \cdot N_{RB}^{PRS}} - {1\mspace{20mu} m^{\prime}}} = {m + N_{RB}^{\max,{DL}} - N_{RB}^{PRS}}}} \right.$

In Equation 4 or Equation 5, N_(RB) ^(PRS) can be configured by higherlayers, and a cell-specific frequency shift ν_(shift) can be given asν_(shift)=N_(cell) ^(ID) mod 6.

FIG. 6 and FIG. 7 show an example of a PRS pattern mapped to a resourceblock.

FIG. 6 shows a case of mapping a PRS to a resource block in a normal CPcase. FIG. 6A shows a PRS pattern when the number of PBCH antenna portsis 1 or 2. FIG. 6B shows a PRS pattern when the number of PBCH antennaports is 4. FIG. 7 shows a case of mapping a PRS to a resource block inan extended CP case. FIG. 7A shows a PRS pattern when the number of PBCHantenna ports is 1 or 2. FIG. 7B shows a PRS pattern when the number ofPBCH antenna ports is 4. The PRS is mapped to a diagonal pattern in aresource block.

Table 1 shows a cell-specific subframe configuration period T_(PRS) anda cell-specific subframe offset Δ_(PRS). A PRS configuration indexI_(PRS) can be given by a higher layer. The PRS can be transmitted onlyin a downlink subframe configured for PRS transmission. The PRS cannotbe transmitted in a special subframe of a TDD system. The PRS can betransmitted in N_(PRS) contiguous downlink subframes, and N_(PRS) can begiven by the higher layer. In addition, among the N_(PRS) contiguousdownlink subframes, (10×n_(f)+└n_(s)/2┘−Δ_(PRS)) mod T_(PRS)=0 can besatisfied for a first subframe.

TABLE 1 PRS PRS periodicity PRS subframe configuration T_(PRS) offsetΔ_(PRS) Index I_(PRS) (subframes) (subframes)  0-159 160 I_(PRS) 160-479320 I_(PRS) − 160  480-1119 640 I_(PRS) − 480 1120-2399 1280   I_(PRS) −1120 2400-4095 Reserved

A method of estimating a location of a UE can be classified into aGPS-based method and a terrestrial positioning-based method. Theterrestrial positioning-based method estimates the location of the UE byusing a timing difference of signals transmitted from BSs. Signals mustbe received from at least three BSs. Although this method has lowerlocation estimation performance in comparison with the GPS-based method,this method can be used in most of environments. A signal received fromthe BS may be a synchronization signal or a reference signal (RS).

FIG. 8 shows an example of operating an observed time difference ofarrival (OTDOA) method as a terrestrial positioning-based method. A UEmeasures a reference clock on the basis of a subframe transmitted in aserving cell currently receiving a service. A subframe is received froma neighbor cell 2 at a time elapsed by a TDOA 2 from the referenceclock. A subframe is received from a neighbor cell 1 at a time elapsedby a TDOA 1, longer than the TDOA 2, from the reference clock. A PRS maybe included in each subframe transmitted from multiple cells.

The UE can estimate the location of the UE according to a difference ina reception time of a PRS transmitted from the serving cell and theneighbor cell. A reference signal time difference (RSTD) between aneighbor cell j and a reference cell i can be defined asT_(subframeRxj)−T_(subframeRxi), and can be found in the section 5.1.12of 3GPP TS 36.214 V9.1.0 (2010-03) 5.1.12. T_(subframeRxj) denotes atime at which the UE receives a start part of one subframe from the cellj. T_(subframeRxi) denotes a time at which a start part of correspondingone subframe is received from the cell i, which is the closest in timeto the subframe received from the cell j by the UE. A reference pointfor measuring the RSTD may be an antenna connector of the UE.

FIG. 9 shows another example of operating a downlink OTDOA method as aterrestrial positioning-based method. A location of a UE can beestimated by solving a linearlized equation by the use of a Taylorseries expansion. This can be found in [Y. Chan and K. Ho, “A simple andefficient estimator for hyperbolic location,” IEEE Trans. SignalProcessing, vol. 42, pp. 1905-1915, August 1994].

If the location of the UE is estimated by using the downlink OTDOAmethod, the UE and an enhanced serving mobile location center (E-SMLC)can mutually exchange information according to an LTE positioningprotocol (LPP). The UE can measure OTDOA of RSs transmitted by multipleBSs and transmit a measurement result to the E-SMLC through the LPP. TheE-SMLC can transmit assistance data required by the UE for themeasurement to the UE through the LPP.

FIG. 10 shows an example of an assistance data exchange process betweena UE and an E-SMLC through an LPP. Through the assistance data exchangeprocess, the UE can request the E-SMLC to transmit assistance datarequired for location estimation, and can receive the assistance datafrom the E-SMLC. This can be found in the section 5.2.1 of 3GPP TS36.355V9.2.1 (2010 June).

In step S50, the UE transmits an assistance data request message to theE-SMLC. In step S51, the E-SMLC transmits an assistance data providemessage including the assistance data to the UE. The transmittedassistance data may be matched to the assistance data request messagerequested by the UE or may be a subset of the message. In step S52, theE-SMLC can transmit one or more additional assistance data providemessages including additional assistance data to the UE. The additionalassistance data may also be matched to the assistance data requestmessage requested by the UE or may be a subset of the message.Meanwhile, a finally transmitted assistance data provide message mayinclude information indicating the end of the assistance data exchange.

In the downlink OTDOA method, the assistance data provide message can betransmitted using an OTDOA assistance data provide (i.e.,OTDOA-ProvideAssistanceData) information element (IE). Table 2 shows anexample of the OTDOA-ProvideAssistanceData IE. This can be found in thesection 6.5.1 of 3GPP TS36.355 V9.4.0 (2010 December).

TABLE 2 -- ASN1START OTDOA-ProvideAssistanceData ::= SEQUENCE {otdoa-ReferenceCellInfo OTDOA-ReferenceCellInfo OPTIONAL,otdoa-NeighbourCellInfo OTDOA-NeighbourCellInfoList OPTIONAL,otdoa-Error OTDOA-Error OPTIONAL, ... } -- ASN1STOP

Referring to Table 2, the OTDOA-ProvideAssistanceData IE includes anOTDOA reference cell information (i.e., OTDOA-ReferenceCellInfo) IE andan OTDOA neighbor cell information list (i.e.,OTDOA-NeighbourCellInfoList) IE. In this case, if the UE cannot acquireany SFN from any cell, a criterion for OTDOA measurement cannot bedetermined, and thus OTDOA measurement cannot be performed, therebydisabling UE location estimation. Therefore, a solution of this problemcan be proposed by defining at least one cell for which an SFN can beobtained by the UE or by including it to a neighbor cell list.

Table 3 shows an example of the OTDOA-ReferenceCellInfo IE. The E-SMLCcan transmit information of a reference cell used as a criterion ofOTDOA measurement to the UE according to the OTDOA-ReferenceCellInfo IE.

TABLE 3 -- ASN1START OTDOA-ReferenceCellInfo ::= SEQUENCE { physCellIdINTEGER (0..503), cellGlobalId ECGI OPTIONAL, -- Need ON earfcnRefARFCN-ValueEUTRA OPTIONAL, --Cond NotSameAsServ0 antennaPortConfigENUMERATED {ports1-or-2, ports4, ... } OPTIONAL, -- Cond NotSameAsServ1cpLength ENUMERATED { normal, extended, ... }, prsInfo PRS-InfoOPTIONAL, -- Cond PRS ... } -- ASN1STOP

In Table 3, PRS information (i.e., PRS-Info) IE indicates a PRSconfiguration of a reference cell. Table 4 shows an example of thePRS-Info IE.

TABLE 4 -- ASN1START PRS-Info ::= SEQUENCE { prs-Bandwidth ENUMERATED {n6, n15, n25, n50, n75, n100, ... }, prs-ConfigurationIndex INTEGER(0..4095), numDL-Frames ENUMERATED {sf-1, sf-2, sf-4, sf-6, ...}, ...,prs-MutingInfo-r9 CHOICE { po2-r9 BIT STRING (SIZE(2)), po4-r9 BITSTRING (SIZE(4)), po8-r9 BIT STRING (SIZE(8)), po16-r9 BIT STRING(SIZE(16)), ... } OPTIONAL -- Need OP } -- ASN1STOP

In Table 4, a prs-Bandwidth field indicates a bandwidth used for PRStransmission.

The prs-Bandwidth field can indicate the number of resource blocks forPRS transmission. A prs-ConfigurationIndex field indicates a PRSconfiguration index I_(PRS) of Table 1. A numDL-Frames field indicatesthe number N_(PRS) of contiguous downlink subframes in which the PRS istransmitted. A value of the numDL-Frames field may be 1, 2, 4, or 6.

In Table 4, a prs-MutingInfo field indicates a PRS muting configurationof a reference cell. The PRS muting configuration can be defined by aperiodic PRS muting sequence having a period T_(REP). T_(REP) can bedefined as the number of PRS occasions, and may have any one value among2, 4, 8, and 16. Each PRS occasion can be defined as N_(PRS) contiguousdownlink subframes in which the PRS is transmitted. T_(REP) is equal toa length of a selected bit string indicating a PRS muting sequence. Forexample, if T_(REP)=2, the length of the bit string is also 2. If a bitvalue of the PRS muting sequence is 0, PRS transmission is muted in acorresponding PRS occasion. A PRS muting pattern based on the PRS mutingsequence can be configured on the basis of a case where a system framenumber (SFN) of a reference cell is 0. That is, a first bit of the PRSmuting sequence may correspond to a first PRS occasion that starts afterthe SFN of the reference cell becomes 0. The PRS muting sequence isvalid for all subframes after the UE receives the PRS muting informationfield. If the PRS muting information field is not provided, the UE mayassume that PRS muting is not applied to the reference cell.

Table 5 shows an example of an OTDOA neighbor cell information list(i.e., OTDOA-NeighbourCellInfoList) IE. The E-SMLC can transmit neighborcell information required for OTDOA measurement to the UE according tothe OTDOA-NeighbourCellInfo IE. In the OTDOA-NeighbourCellInfoList IE,information on each neighbor cell can be sorted in a descending order ofimportance of neighbor cells measured by the UE. That is, in OTDOAmeasurement, a neighbor cell having a highest priority may be a firstcell. The UE measures the OTDOA according to an order of cells in theOTDOA-NeighbourCellInfoList IE provided by the E-SMLC. Meanwhile, in theOTDOA-NeighbourCellInfoList IE, a slot number offset field (i.e.,slotNumberOffset) and an expected RSTD field (i.e., expectedRSTD) can bedefined relatively for each cell on the basis of a reference cell.

TABLE 5 -- ASN1START OTDOA-NeighbourCellInfoList ::= SEQUENCE (SIZE(1..maxFreqLayers)) OF OTDOA-NeighbourFreqInfo OTDOA-NeighbourFreqInfo::= SEQUENCE (SIZE (1..24)) OF OTDOA-NeighbourCellInfoElementOTDOA-NeighbourCellInfoElement ::= SEQUENCE { physCellId INTEGER(0..503), cellGlobalId ECGI OPTIONAL, -- Need ON earfcn ARFCN-ValueEUTRAOPTIONAL, -- Cond NotSameAsRef0 cpLength ENUMERATED {normal, extended,...} OPTIONAL, -- Cond NotSameAsRef1 prsInfo PRS-Info OPTIONAL, -- CondNotSameAsRef2 antennaPortConfig ENUMERATED {ports-1-or-2, ports-4, ...}OPTIONAL, -- Cond NotsameAsRef3 slotNumberOffset INTEGER(0..31)OPTIONAL, -- Cond NotSameAsRef4 prs-SubframeOffset INTEGER (0..1279)OPTIONAL, -- Cond InterFreq expectedRSTD INTEGER (0..16383),expectedRSTD-Uncertainty INTEGER (0..1023), ... } maxFreqLayers INTEGER::= 3 -- ASN1STOP

Referring to Table 5, OTDOA neighbor cell information of each neighborcell includes a PRS-Info IE similarly to the OTDOA-ReferenceCellInfo IEof Table 3. Accordingly, PRS muting can be configured with respect toeach neighbor cell as shown in Table 4.

Meanwhile, if the location of the UE is estimated by the downlink OTDOAmethod, the BS and the E-SMLC can mutually exchange information by anLPP annex (LPPa). The LPPa provides a control plane radio network layersignaling process between the BS and the E-SMLC.

FIG. 11 shows an example of a data exchange process between a BS and anE-SMLC through an LPPa. This can be found in the section 8.2.5 of 3GPPTS36.455 V9.2.0 (2010 June).

In step S60, the E-SMLC transmits an OTDOA information request messageto a BS. The E-SMLC initializes the information exchange process betweenthe E-SMLC and the BS by transmitting the OTDOA information requestmessage. In step S61, the BS transmits an OTDOA information responsemessage to the E-SMLC. The OTDOA information response message includesOTDOA cell information of cells related to estimation of a location of aUE.

The BS can operate by using parameters such as a PRS configuration indexconfigured for each BS, an SFN initialization time, a PRS mutingconfiguration, etc. Table 6 shows an example of each cell's OTDOA cellinformation transmitted by the UE.

TABLE 6 IE/Group Name Presence Range IE type and reference Semanticsdescription OTDOA Cell 1 to Information <maxnoOTDOAtypes> >CHOICE OTDOAM Cell Information Item >>PCI M INTEGER (0 . . . 503, Physical Cell ID .. .) >>Cell ID M ECGI 9.2.6 >>TAC M OCTET STRING(2) Tracking AreaCode >>EARFCN M INTEGER (0 . . . 65535) Corresponds to N_(DL) for FDDand N_(DL/UL) for TDD in ref. [5] >>PRS Bandwidth M ENUMERATEDTransmission (bw6, bw15, bw25, bandwidth of PRS bw50, bw75, bw100, . ..) >>PRS M INTEGER (0 . . . 4095) PRS Configuration Configuration IndexIndex, ref [6] >>CP Length M ENUMERATED Cyclic prefix length of (Normal,Extended, . . .) the PRS >>Number of DL M ENUMERATED (sf1, Number ofconsecutive Frames sf2, sf4, sf6, . . .) downlink subframes N_(PRS) withPRS, ref [6] >>Number of M ENUMERATED Number of used Antenna Ports(n1-or-n2, n4, . . .) antenna ports, where n1-or-n2 corresponds to 1 or2 ports, n4 corresponds to 4 ports >>SFN Initialisation M BIT STRING(64) Time in seconds Time relative to 00:00:00 on 1 Jan. 1900 where theinteger part is in the first 32 bits and the fraction part in the last32 bits >>E-UTRAN Access M 9.2.8 The configured Point Position estimatedgeographical position of the antenna of the cell. >>PRS Muting M 9.2.9The configuration of Configuration positioning reference signals mutingpattern, when applicable

Meanwhile, when the UE recognizes each cell's PRS muting sequence andPRS muting pattern, an SFN unknown problem may occur. When the UE knowsthe PRS muting sequence and the PRS muting pattern on the basis of theSFN of the reference cell but does not know the SFN of the referencecell, the SFN unknown problem may occur. For example, the PRS mutingpattern can be configured starting from a time at which the SFN of thereference cell becomes 0. In this case, if the UE does not know the SFNof the reference cell, the UE cannot know whether a next PRS occasion ismuted or not. In general, the UE knows only an SFN of a serving cell inwhich a service of the UE is provided. Since the reference cell does notcoincide with the serving cell in a process of performing a handover orthe like of the UE, the SFN unknown problem may frequently occur.

FIG. 12 and FIG. 13 show an example of a case where an SFN unknownproblem occurs.

In FIG. 12 and FIG. 13, it is assumed that a serving cell is included inan OTDOA neighbor cell list. That is, the serving cell does not coincidewith a reference cell. In addition, it is also assumed that there is nopropagation delay, and the UE knows only the SFN of the serving cell.The UE can estimate a PRS occasion by using a slot number offset and anSFN of the serving cell which is one of neighbor cells, and can measurean RSTD by using the estimated PRS occasion. However, since the UE doesnot know a time at which an SFN of the reference cell is 0, the UEcannot know whether a next PRS occasion is muted or not. Accordingly,the RSTD cannot be properly measured.

In FIG. 12, a PRS configuration index I_(PRS) is 0 for both of theserving cell and the reference cell. An SFN offset of the serving celland the reference cell is 320 ms. A muting sequence of the serving cellis 10₍₂₎, and a muting sequence of the reference cell is 01₍₂₎. Sincethe UE does not know a time at which the SFN of the reference cellbecomes 0, the UE cannot know whether a PRS occasion happened aftermeasuring of the RSTD is muted or not.

In FIG. 13, a PRS configuration index I_(PRS) of a serving cell is 0,and a PRS configuration index I_(PRS) of a reference cell is 130. An SFNoffset of the serving cell and the reference cell is 30 ms. A mutingsequence of the serving cell is 10₍₂₎, and a muting sequence of thereference cell is 01₍₂₎. Since the UE does not know a time at which theSFN of the reference cell becomes 0, the UE cannot know whether a PRSoccasion happened after measuring of the RSTD is muted or not.

Meanwhile, the SFN unknown problem may also occur in case of anasynchronous network in which multiple cells are asynchronous. In caseof a synchronous network in which the multiple cells are synchronous,the UE can predict the SFN of the reference cell on the basis of theserving cell receiving a service, and thus can know a muting pattern ofa PRS transmitted by each cell. However, in case of the asynchronousnetwork, there is a possibility that the UE cannot recognize the SFN ofthe reference cell, and thus the UE cannot know a time at which the PRStransmitted by each cell is muted. In this case, the UE must acquire SFNinformation of the reference cell by decoding a PBCH. Therefore, acomplexity of the UE is increased, and if a signal to interference noiseratio (SINR) of a signal received from the reference cell is small,decoding performance of the PBCH is decreased, and thus the SFNinformation of the reference cell may not be properly acquired.

Accordingly, there is a need for a method for solving the SFN knownproblem.

1) At a time in which the UE receives PRS muting information, a PRSmuting sequence and a PRS muting pattern can be configured on the basisof an SFN of a cell for which the SFN can be obtained by the UE. The UEcan recognize a PRS muting pattern of each cell on the basis of an SFNof a cell for which the SFN can be acquired at a time of receiving thePRS muting information. In this case, the cell for which the SFN can beobtained by UE may be a serving cell. A PRS muting pattern based on thePRS muting sequence can be configured on the basis of a case in whichthe SFN of the cell for which the SFN can be obtained by the UE is 0.That is, a first bit of the PRS muting sequence may correspond to afirst PRS occasion that starts after the SFN of the cell for which theSFN can be obtained by the UE becomes 0. Alternatively, the first bit ofthe PRS muting sequence may correspond to a first PRS occasion thatstarts after an SFN of a serving cell becomes 0 when the UE receives PRSmuting information. Accordingly, the SFN unknown problem can be solvedexcept for a case in which the UE performs a handover.2) A PRS muting sequence and a PRS muting pattern can be configured onthe basis of a first PRS occasion received by the UE. That is, the UEdoes not require an SFN of any one cell in which a PRS is transmitted,and can recognize the PRS muting sequence and the PRS muting pattern onthe basis of a time at which PRS muting information is received.Accordingly, the first bit of the PRS muting sequence may correspond toa first PRS occasion received after the UE receives the PRS mutinginformation. Alternatively, the first bit of the PRS muting sequence maycorrespond to a first PRS occasion received after OTDOA assistance datais delivered to the UE by using the OTDOA-ProvideAssistanceData IE.3) The PRS muting sequence and the PRS muting pattern can be configuredon the basis of the SFN of the reference cell, and the UE can acquirethe SFN by decoding the PBCH transmitted from the reference cell.Alternatively, the PRS-Info IE may additionally include an SFN offsetfield or an SFN itself, and thus the UE can estimate the PRS mutingsequence and the PRS muting pattern by acquiring the SFN of thereference cell. An SFN offset field or an SFN value can be added to thePRS-Info IE for the serving cell or the reference cell. Alternatively,the UE can acquire an SFN of a cell for which the SFN can be obtained bythe UE and an SFN of the reference cell from the SFN or an SFN offsetfield of the reference cell, and thus can estimate the PRS mutingsequence and the PRS muting pattern.4) All of bits constituting the PRS muting sequence can be configuredwith 0 or 1. If the PRS muting sequence is ‘11 . . . ’, the PRS istransmitted always in all PRS occasions, and if the PRS muting sequenceis ‘00 . . . ’, PRS transmission is always muted in all PRS occasions.Accordingly, the SFN unknown problem can be solved without having toidentify the SFN of the reference cell in order for the UE to know thePRS muting pattern.

FIG. 14 shows the proposed message transmission method for locationestimation according to an embodiment of the present invention.

In step S100, a UE receives a PRS from each of a reference cell and atleast one neighbor cell. In step S110, the UE receives from an E-SMLC anassistance data provide message including a reference cell PRS mutingsequence indicating a muting pattern of a PRS transmitted by thereference cell and a neighbor cell PRS muting sequence indicating amuting pattern of a PRS transmitted by at least one neighbor cell. Instep S120, the UE transmits to the E-SMLC an RSTD measured on the basisof a PRS received from the reference cell and the at least one neighborcell. In this case, the reference cell muting sequence and the neighborcell muting sequence can be configured by using various methodsdescribed above.

FIG. 15 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A BS 800 may include a processor 810, a memory 820 and a radio frequency(RF) unit 830. The processor 810 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 810. The memory 820 is operatively coupled with the processor810 and stores a variety of information to operate the processor 810.The RF unit 830 is operatively coupled with the processor 810, andtransmits and/or receives a radio signal.

A user equipment 900 may include a processor 910, a memory 920 and a RFunit 930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The RF unit 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for measuring, by a user equipment (UE),a reference signal time difference (RSTD) in a wireless communicationsystem, the method comprising: receiving assistance data for observedtime difference of arrival (OTDOA), including first position referencesignal (PRS) information for an assistance data reference cell andsecond PRS information for two other cells from a location server, thefirst PRS information includes a PRS muting sequence for the assistancedata reference cell and the second PRS information includes two PRSmuting sequences, one for each of the two other cells, wherein a firstbit of each PRS muting sequence corresponds to a first PRS occasion thatstarts after a system frame number (SFN) of the assistance datareference cell becomes 0; receiving a PRS for each of the assistancedata reference cell and the two other cells based on the PRS mutingsequences; and measuring the RSTD based on the received PRSs.
 2. Themethod of claim 1, wherein the assistance data reference cell is a cellfor which the SFN can be obtained by the UE.
 3. The method of claim 1,wherein the assistance data reference cell is a neighbor cell.
 4. Themethod of claim 1, further comprising transmitting the RSTD to thelocation server.
 5. The method of claim 1, wherein the RSTD is arelative delay of a reference subframe including the PRS received fromthe assistance data reference cell and reference subframes that includethe PRSs received from the two other cells and corresponding to thereference subframe.
 6. A user equipment (UE) comprising: a memory; aradio frequency (RF) unit; and a processor coupled to the memory and theRF unit, and configured to: control the RF unit to receive assistancedata for observed time difference of arrival (OTDOA), including firstposition reference signal (PRS) information for an assistance datareference cell and second PRS information for two other cells from alocation server, the first PRS information includes a PRS mutingsequence for the assistance data reference cell and the second PRSinformation includes two PRS muting sequences, one for each of the twoother cells, wherein a first bit of each PRS muting sequence correspondsto a first PRS occasion that starts after a system frame number (SFN) ofthe assistance data reference cell becomes 0; control the RF unit toreceive a PRS for each of the assistance data reference cell and the twoother cells based on the PRS muting sequences; and measure a referencesignal time difference (RSTD) based on the received PRSs.
 7. The UE ofclaim 6, wherein the assistance data reference cell is a cell for whichthe SFN can be obtained by the UE.
 8. The UE of claim 6, wherein theassistance data reference cell is a neighbor cell.
 9. The UE of claim 6,wherein the processor is further configured to control the RF unit totransmit the RSTD to the location server.
 10. The method of claim 1,wherein the PRS muting sequences for the two other cells are configuredbased on the SFN of the assistance data reference cell.
 11. The UE ofclaim 6, wherein the PRS muting sequences for the two other cells areconfigured based on the SFN of the assistance data reference cell.